How can I initialize or update value of a variable, like with UIKit, in SwiftUI?

Question

For example in the code below I can update my value with action of a Button or with .onAppear() of Text, and there is some other ways. But I am interested if there is a way or tech for coding like this:

struct ContentView: View {
    
    @State private var valueOfA: String?
    
    var body: some View {
        valueOfA = "Magic!" // ← Here(I know it is impossible but if there is a way of this coding?)
        
        Button("change") { valueOfA = "omid" }
        
        Button("nil") { valueOfA = nil }
        
        Text(valueOfA ?? "")
            .onAppear {
                valueOfA = "Some Value"
            }
    }
}

The problem here is that you are changing a @State variable in the body. This will cause an infinite loop of the view trying to update itself. What do you want instead? — George
– George, Commented Nov 8, 2020 at 0:07
What do you want to achieve? Good Question! Some times we are using GeometryReader for some reason I wanted update my values without using .onAppear or .onChange(), because "value in" is not reachable out side of GeometryReader, and other part of program need those data, I thought if we code just update those like UIKit mode — swiftPunk
– swiftPunk, Commented Nov 8, 2020 at 0:12
It might help if you create an actual example with GeometryReader so we can see the big picture here. — pawello2222
– pawello2222, Commented Nov 8, 2020 at 0:25
@pawello2222: my Goal is currently to find Answer of Question, what ever if we can find or not, I want be sure about the possibility of initialize or update value of a variable, like with UIKit, in SwiftUI? debugging of this project is not important for me. As you said I wanted give a pic — swiftPunk
– swiftPunk, Commented Nov 8, 2020 at 3:33

Asperi · Accepted Answer · 2020-11-08 05:44:25Z

2

Well... it is really like with Alice...

One has got into mind... probably you wanted this:

struct ContentView: View {
    
    @State private var valueOfA: String?
    
    var body: some View {
        let valueOfA = self.valueOfA ?? "Magic!"
        
        Button("change") { self.valueOfA = "omid" }
        
        Button("nil") { self.valueOfA = nil }
        
        Text(valueOfA)
            .onAppear {
                self.valueOfA = "Some Value"
            }
    }
}

... and by the way we do not change frame in draw(_ rect:) in UIKit, yes?, but you try to do similar to that.

answered Nov 8, 2020 at 5:44

Asperi

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